Some examples of hypoelliptic operators of infinitely degenerate type (Q1327624)

Hypoellipticity of a special class of degenerate elliptic second order partial differential operators with coefficients flat at the origin is studied. The proof of both negative and positive results is based on an interesting idea of \textit{G. R. Aleksandryan} [Sov. J. Contemp. Math. Anal., Arm. Acad. Sci. 19, No. 3, 33-46 (1984; Zbl 0599.35111)] to use degenerate hypergeometric functions in investigating weakly hyperbolic equations with flat coefficients at 0.